docs: def _get_stddevs(self, C, stddev_types, num_sites, mag_conversion_sigma):
          """
          Return total standard deviation.
          """
          assert all(stddev_type in self.DEFINED_FOR_STANDARD_DEVIATION_TYPES
                     for stddev_type in stddev_types)
  
          sigma = np.zeros(num_sites) + C['sigma'] * np.log(10)
          sigma = np.sqrt(sigma ** 2 + (C['a'] ** 2) * (mag_conversion_sigma ** 2))
          stddevs = [sigma for _ in stddev_types]
  
          return stddevs